1. Field of the Invention
The present invention relates to a random number generating device.
2. Related Art
Random numbers are used to perform encryption and authentication to ensure information security. As more and more mobile devices are used recently, there has been an increasing demand for small-sized, high-speed random number generating devices. Conventionally, pseudorandom numbers have been used in small-sized terminal devices such as mobile devices.
However, to protect personal information, a more sophisticated security technique is now required. To avoid unauthorized decryption, more unpredictable true random numbers need to be generated. In generating true random numbers, random noise generated through a physical phenomenon can be effectively used. By a known technique for generating random noise based on a physical phenomenon, fluctuations of diode currents are utilized. By this method, however, a large amplifier circuit is required to amplify fine while noise. With a large amplifier circuit, it is difficult to form a small-sized random number generating device.
There have also been small-sized random number generating devices that have SiN MOSFETs as random noise generating elements (see M. Matsumoto, et al., “International Conference on Solid State Devices and Materials”, SSDM (Solid State Device and Materials) 2006, p.p. 280-281, 2006, for example). In such a SiN MOSFET, only a very thin tunnel insulating film is interposed between the channel and traps based on dangling bonds in a nonstoichiometric SiN film. When a fixed voltage is applied to the gate electrode, random electron charging and discharging are caused between the channel and the trap due to heat fluctuations. Accordingly, by applying a fixed voltage to the gate electrode, the conductivity of the channel region is randomly varied with the amount of charges captured by the trap based on the dangling bonds existing in the nonstoichiometric SiN film. As a result, the current flowing through the channel randomly varies, to generate random noise. This random noise is converted into digital random numbers. In this manner, random numbers can be generated.
There have also been small-sized random number generating devices that have MOSFETs as random noise generating elements. Such a MOSFET has a set of conductive Si fine particles formed on the tunnel insulating film (see US 2005/0180219 A1, for example). When a fixed voltage is applied to the gate electrode of the MOSFET, random electron charging and discharging are caused between the channel and the set of conductive Si fine particles due to heat fluctuations. Random noise is then generated in the drain current flowing through the channel.
Normally, it is preferable that random numbers are generated at a high generating rate. However, the above described random noise generating elements disclosed by M. Matsumoto, et al., in “International Conference on Solid State Devices and Materials”, SSDM (Solid State Device and Materials) 2006, p.p. 280-281, 2006, and in US 2005/0180219 A1 are need to generate high-quality random numbers at an expected high-speed generating rate.
As described above, to further improve information security, there is a demand for small-sized random number generating devices that can generate high-quality random numbers at higher speeds. However, it has been difficult to form a random number generating device that can generate high-quality random numbers at a high speed.